The invention relates to hydroxy group-containing diesters of acrylic acids, especially dimethacrylates, and their use in dental material, especially in tooth filling material.
Tooth filling materials made of plastics have been known for many years. The first of these materials consisted of mixtures of monomeric and polymeric methylmethacrylate which, upon the addition of a catalyst or of a system consisting of catalyst and accelerator, hardened within a few minutes under the temperature conditions prevailing within the mouth.
An improvement of the mechanical characteristics of these filling materials was achieved by the addition of finely divided fillers such as quartz or aluminum silicates, and an improvement of the aesthetic effect was achieved by the development of new catalyst systems which cause no discoloration.
Tooth filling materials must harden within a reasonable time, must be biologically compatible, and must provide fillings having good strength characteristics. One special problem is the shrinkage of the material which occurs during polymerization. This results in the development of a shrinkage gap or marginal gap between the wall of the tooth cavity and the filling, which greatly accelerates the development of secondary caries.
Through the development of filling materials known as "composites," which are composed of a finely divided inorganic filler treated with a silane to improve adhesion between the filler particles and the plastic, a polymerizable monomeric compound as binding agent, a catalyst and, in some cases, accelerators and other additives such as pigments, for example, the plastic-based tooth filling materials have been so improved that they are in no way inferior in importance to the silicate cements, and in some ways are even more appropriate than the latter, especially for visible fillings in the front teeth.
The first of these new materials was developed by Rafael L. Bowen and is described in U.S. Pat. No. 3,066,112. It contains as the monomeric binding agent a diacrylate or dimethacrylate containing hydroxy groups which is prepared by the reaction of a bisphenol with glycidyl acrylate or glycidyl methacrylate. The reaction product formed by bisphenol A and glycidyl methacrylate, known as bis-GMA, is considered to be especially suitable. It is contained in a number of commercial products as a monomeric binding agent. Dental fillings made therewith have good mechanical strength. The high viscosity of the monomeric binding agents, however, makes them difficult to handle.
Esters of acrylic acids having a low viscosity, which are suitable for use in dental filling materials, are known from U.S. Pat. No. 3,730,947. These are especially 1,3-bis-(2-hydroxy-3-acryloyloxypropoxy)-benzene and the corresponding methacryloyloxy derivative.
These compounds do have a lower viscosity than bis-GMA, which facilitates handling them, but their lower molecular weight produces a greater shrinkage in polymerization and consequently a greater amount of shrinkage gaps or marginal gaps.